
public class S {

	public static void main(String[] args) {
		int b =0;
		for (int i = 0; i <=100; i++) {
			int a;
			a=i%2;
			if(a==0) {
				b=i+b;
				if(i==100) {
					System.out.println(b);
				}
			}
		}
	}

}
